linux-kernel - [ 68/95] ARM: 7355/1: perf: clear overflow flag when disabling counter on ARMv7 PMU

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Message-Id: <20120309190207.817875694@linuxfoundation.org>
Date:	Fri, 09 Mar 2012 11:03:10 -0800
From:	Greg KH <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Ming Lei <tom.leiming@...il.com>,
	Will Deacon <will.deacon@....com>,
	Russell King <rmk+kernel@....linux.org.uk>
Subject: [ 68/95] ARM: 7355/1: perf: clear overflow flag when disabling counter on ARMv7 PMU

3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Will Deacon <will.deacon@....com>

commit 99c1745b9c76910e195889044f914b4898b7c9a5 upstream.

When disabling a counter on an ARMv7 PMU, we should also clear the
overflow flag in case an overflow occurred whilst stopping the counter.
This prevents a spurious overflow being picked up later and leading to
either false accounting or a NULL dereference.

Reported-by: Ming Lei <tom.leiming@...il.com>
Signed-off-by: Will Deacon <will.deacon@....com>
Signed-off-by: Russell King <rmk+kernel@....linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/arm/kernel/perf_event_v7.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/arch/arm/kernel/perf_event_v7.c
+++ b/arch/arm/kernel/perf_event_v7.c
@@ -878,6 +878,11 @@ static inline int armv7_pmnc_disable_int
 
 	counter = ARMV7_IDX_TO_COUNTER(idx);
 	asm volatile("mcr p15, 0, %0, c9, c14, 2" : : "r" (BIT(counter)));
+	isb();
+	/* Clear the overflow flag in case an interrupt is pending. */
+	asm volatile("mcr p15, 0, %0, c9, c12, 3" : : "r" (BIT(counter)));
+	isb();
+
 	return idx;
 }
 


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